The present invention relates to temperature control of semiconductor substrates during processing and, more particularly, to cold-wall reactors and methods for achieving better temperature uniformity during high temperature processing.
Chemical vapor deposition (CVD) is a well known process in the semiconductor industry for forming thin films of materials on substrates, such as silicon wafers. In a CVD process, one or more substrates are placed on a wafer support inside a chamber that forms part of a reactor (i.e., within a reaction chamber of the reactor), and gaseous precursors of the material to be deposited on the substrates are supplied to the substrates to form a thin film of the material by chemical reaction. Typically, CVD processes are conducted at elevated temperatures (e.g., greater than 500xc2x0 C.) to accelerate the chemical reaction and to produce high quality films. Through subsequent processes, these layers are used to form integrated circuits.
Various process parameters must be carefully controlled to ensure the high quality of the layers. One such critical parameter is the temperature of the wafer during each process step.
Substrates can be heated using various techniques, including resistance heating, induction heating and radiant heating. Among these, radiant heating is the most efficient technique for temperature cycling and, thus, is the currently favored method for high temperature processes. Radiant heating involves positioning lamps within high-temperature reactors. Unfortunately, radiant energy has a tendency to create non-uniform temperature distributions, or xe2x80x9chot spots,xe2x80x9d in the wafer due to the use of localized sources and the consequent focusing and interference effects.
If the temperature varies across the surface of the wafer, material deposition can occur unevenly across the wafer, and the thickness of the deposited layers will not be uniform. Similarly, non-uniformity or instability of temperature across a wafer during other thermal treatments can affect the uniformity of resulting structures. There are many other processes for which temperature control is critical, including oxidation, nitridation, dopant diffusion, sputter depositions, photolithography, dry etching, plasma processes, and high temperature anneals.
To overcome the aforementioned problems, reactors have been constructed in which the wafer is rotated during processing. Such reactors may include a circular rotatable support structure, upon which the wafer is situated. The support structure rotates the wafer about its central axis to reduce the temperature non-uniformity across the wafer.
The lamps within the reactor can also be positioned in a manner that will facilitate controlling the temperature in various locations within the reaction chamber. For instance, in some configurations, the lamps generally are linear in design and are arranged in a pair of crossing arrays. The grid resulting from the crossing array configuration facilitates some control over the temperature uniformity of the wafer by allowing adjustment of the power that is delivered to a particular lamp or group of lamps.
Unfortunately, the configuration of the radiant heating lamps may present further temperature non-uniformity problems. For example, the radiant heating patterns generated by the lamps may closely resemble the pattern or position of the lamps within or around the chamber. Furthermore, heat may be reflected off of or re-radiated from the surface of the wafer and the walls of the chamber in a consistent pattern, thus creating concentrated regions of radiation and resulting in non-uniform heating of the wafer.
In an effort to provide a more uniform temperature distribution across the wafer, reflectors have been mounted behind the lamps to indirectly illuminate the wafer. The reflectors can be roughened to diffuse the radiation redirected by the reflectors towards the substrate. The radiation reflected onto the wafer surface is thus made more uniform. U.S. Pat. No. 6,021,152, for example, discloses a system for achieving a more random reflection of radiation from the reflector surface.
Despite improvements in temperature control and reflector technology, radiant heating systems can still produce non-uniform temperatures across wafers being processed. Accordingly, a need exists for a system that achieves more uniform temperatures across semiconductor wafers during processing. Desirably, such a system should be a radiant heating system to maintain the advantages of radiant heating.
In accordance with one aspect of the present invention, a semiconductor processing apparatus is provided, comprising a processing chamber defined by a plurality of walls and a substrate support to support a substrate within the processing chamber. A plurality of radiant heating lamps are positioned outside the processing chamber to heat the substrate through the walls when the substrate is supported on the substrate support. A diffuser is provided between at least one wall of the processing chamber and the substrate when the substrate is supported within the processing chamber. In one embodiment, the diffuser is formed on an inner surface of the at least one wall. The diffuser diffuses radiation incident on the at least one wall of from the substrate.
In accordance with another aspect of the present invention, a method of uniformly heating a substrate is provided. The method comprises positioning the substrate within a processing chamber defined by a plurality of walls. A diffuser is formed on an inner surface of at least one of the walls. The substrate is radiated through the at least one wall to heat the substrate. The diffuser diffuses radiation incident on the at least one wall from the substrate.